They said they believe it's arson and have arrested a 23-year-old woman.

Even as workers boarded up the building, questions remained about why someone would set fire to the day care.

While WISN 12 News was at the scene, a man describing himself as the suspect's boyfriend shared the news of the arrest, saying investigators came to their home early Wednesday morning pounding on the door.

"In the morning, 'Boom, boom, boom,' police take my girlfriend. They say she's being taken for the investigation," the boyfriend said.

He said his girlfriend recently quit her job after some sort of disagreement between her and the owner.

"The owner and supervisor are just very unprofessional. They do a lot of things they shouldn't do at work, cussing, being rude to the children everything. My girlfriend got tired of it and just quit," the boyfriend said.

He said the owner threatened to withhold a paycheck, which eventually came in the mail.

WISN 12 News called the day care for comment but got a voice mail.

In 2009, a day care at the same location was cited by the state for overbilling and had its license suspended when it was known as Little Rascals day care.

PLANS TO FIGHT THIS. A FORMER MILWAUKEE DAYCARE EMPLOYEE IS UNDER ARREST...ACCUSED OF SETTING FIRE TO THE PLACE WHERE SHE USED TO WORK. IN A STORY YOU'LL SEE ONLY ON 12, REPORTER BEN HUTCHISON CAUGHT UP WITH THE SUSPECT'S BOYFRIEND WHO SAYS SHE DIDN'T DO IT. NATS OF INVESTIGATION MILWAUKEE POLICE AND FIREFIGHTERS SPENT MUCH OF THE NIGHT LOOKING FOR CLUES INTO THE CAUSE OF THE FIRE AT THE "EARLY START" ACADEMY AT 55TH AND CENTER. THEY BELIEVE ITS'S ARSON AND HAVE ARRESTED A 23 YEAR OLD FORMER EMPLOYEE FOR THE CRIME. NATS OF BOARDING UP ... EVEN AS WORKERS BOARD UP THE BUILDING ...QUESTIONS REMAIN ABOUT WHY SOMEONE WOULD SET FIRE TO THIS DAYCARE. WHILE 12 NEWS WAS AT THE SCENE , A MAN DESCRIBING HIMSELF AS THE SUSPECTS BOYFRIEND SHARED THE NEWS OF THE ARREST... SAYING INVESTIGATORS CAME TO THEIR HOME EARLY WEDNESDAY MORNING...POUNDING ON THE DOOR. "4:30 IN THE MORNING, BOOM, BOOM, BOOM. POLICE TAKE MY GIRLFRIEND, THEY SAY SHE'S BEING TAKEN FOR THE INVESTIGATION." HE SAYS HIS GIRLFRIEND RECENTLY QUIT HER JOB AFTER SOME SORT OF DISAGREEMENT BETWEEN HER AND THE OWNER. THE OWNER AND SUPERVISOR ARE JUST VERY UNPROFESSIONAL. THEY DO A LOT OF THINGS THEY SHOULDN'T DO AT WORK, CUSSING, BEING RUDE TO THE CHILDREN EVERYTHING. MY GIRLFRIEND GOT TIRED OF IT AND JUST QUIT. HE SAID THE TWO HAD WORDS...WITH THE OWNER THREATENING TO WITHHOLD A PAYCHECK... THAT EVENTUALLY CAME IN THE MAIL...12 NEWS CALLED THE DAYCARE FOR COMMENT...BUT GOT A VOICEMAIL. HI YOU'VE REACHED MISS BROWN WITH EARLY START ACADEMY... THE BOYFRIEND SAYS BELIEVES HE KNOWS WHO'S RESPONSIBLE. I BELIEVE SHE BURNT DOWN THE PLACE AND PUT THE BLAME ON MY GIRLFRIEND FOR NO REASON JUST BECAUSE SHE QUIT. AT 55TH AND CENTER... BEN HUTCHISON, WISN 12 NEWS... BACK IN 2009, A DAYCARE AT THE SAME LOCATION WAS CITED BY THE STATE FOR OVER BILLING AND HAD ITS LICENSE SUSPENDED WHEN IT WAS KNOWN AS